18650 battery issue

[bort617]

i just bought a klarus xt11 on ebay and it came with a charger and two ultrafire 18650 batteries. before and after charging one of the batteries causes the light to strope/flash. any idea as to what the problem is?

 

[lwknight]

Probably the battery is no good. I have several UF 3000 cells that are between junk and no better than the 2400 mah cells.
A lot of lights cut off when the voltage is too low. Light on voltage drops then light off so voltage goes up then light off again ad infinitum.

 

[bort617]

i had a sneaking suspicion that the battery was bad. i messaged the seller so now lets see if he rectifies it.

 

[roadkill1109]

yup, definitely a bad battery. try testing the voltage, might be 1volt or zero voltage = dead battery

 

[MRTdiver]

It is recommended that every Li-ion user buy a digital multi-meter (DMM). Then you can test and verify cell voltage, especially when you put two cells in series so you can verify the voltage matches.

And more advanced uses: HKJ DMM guide

 

[tatasal]

An 'unhealthy' cell will still give you a high voltage on a DMM, but will 'sag' when a load is applied, giving you erratic performance.

In all probability, your XT is fine but your cell is not. Invest in a 'real' 18650